（一）LED grow 从头学 fpga—小实验

module ledflash(LED,CLK,unuse_pins);
    output[3:0] LED;
    input CLK;  //50MHz
    input [100:1] unuse_pins;
    reg [3:0] LED;
    reg [24:0] counter;
   
    initial
      begin
       LED=4'b1111;
       counter=0;
       end
   
    always@(posedge CLK)                                        //
        begin
            counter<=counter+1;                                    //
            if(counter==25'b1_1000_0000_0000_0000_0000_1000)    //25M
                        
                begin
                    LED<=LED+1;
                    counter<=0;
                   
                end
        end
endmodule